Re: Error on arithmetic evaluation of `~0`.

[Greg Wooledge]

On Wed, Dec 19, 2018 at 10:31:36PM -0500, Bize Ma wrote:
> It is also interesting that this fails:
> 
> var=hello; echo "${var[ ~0]}"
> bash: var: bad array subscript
> 
> Isn't `var[0]` valid and equivalent to `var` ?

Yes, but ~0 is not 0.

wooledg:~$ echo $(( ~0))
-1

The issue you're reporting appears to be present in arithmetic contexts
in general, not only arrays:

wooledg:~$ echo $((~0))
bash: /home/wooledg: syntax error: operand expected (error token is 
"/home/wooledg")

It appears that bash is performing tilde expansion when there's no
whitespace in front of the tilde, or bitwise negation if there is
whitespace.